Genes associated with meningococcal capsule complex are also found in Neisseria gonorrhoeae

Functional characterization of the gonococcal polyphosphate pseudo-capsule

Neisseria gonorrhoeae is an exclusively human pathogen able to evade the host immune system through multiple mechanisms. Gonococci accumulate a large portion of phosphate moieties as polyphosphate (polyP) on the exterior of the cell. Although its polyanionic nature has suggested that it may form a protective shield on the cell surface, its role remains controversial. Taking advantage of a recombinant His-tagged polyP-binding protein, the presence of a polyP pseudo-capsule in gonococcus was demonstrated. Interestingly, the polyP pseudo-capsule was found to be present in specific strains only. To investigate its putative role in host immune evasion mechanisms, such as resistance to serum bactericidal activity, antimicrobial peptides and phagocytosis, the enzymes involved in polyP metabolism were genetically deleted, generating mutants with altered polyP external content. The mutants with lower polyP content on their surface compared to the wild-type strains, became sensitive to complement-mediated killing in presence of normal human serum. Conversely, naturally serum sensitive strains that did not display a significant polyP pseudo-capsule became resistant to complement in the presence of exogenous polyP. The presence of polyP pseudo-capsule was also critical in the protection from antibacterial activity of cationic antimicrobial peptide, such as cathelicidin LL-37. Results showed that the minimum bactericidal concentration was lower in strains lacking polyP than in those harboring the pseudo-capsule. Data referring to phagocytic killing resistance, assessed by using neutrophil-like cells, showed a significant decrease in viability of mutants lacking polyP on their cell surface in comparison to the wild-type strain. The addition of exogenous polyP overturned the killing phenotype of sensitive strains suggesting that gonococcus could exploit environmental polyP to survive to complement-mediated, cathelicidin and intracellular killing. Taken together, data presented here indicate an essential role of the polyP pseudo-capsule in the gonococcal pathogenesis, opening new perspective on gonococcal biology and more effective treatments.

Characterization of capsule genes in non-pathogenic Neisseria species

The genus Neisseria comprises a diverse group of commensal bacteria, which typically colonize the mucosal surfaces of humans and other animals. Neisseria meningitidis, the meningococcus, is notable for its potential to cause invasive meningococcal disease (IMD) in humans; however, IMD is comparatively rare, and meningococci normally colonize the nasopharynx asymptomatically. Possession of a polysaccharide capsule has been shown to be a prerequisite for disease in almost all IMD cases, and was previously considered unique to N. meningitidis, and potentially acquired by horizontal genetic transfer (HGT). Nevertheless, the capsule must also have some role in asymptomatic colonization and/or transmission, consistent with the existence of six non-disease-associated meningococcal capsule serogroups. In this study, full complements of putative capsule genes were identified in non-pathogenic Neisseria species, including Neisseria subflava and Neisseria elongata. These species contained genes for capsule transport and translocation homologous to those of N. meningitidis, as well as novel putative capsule synthesis genes. Phylogenetic analyses were consistent with the proposal that these genes were acquired by the meningococcus through HGT. In contrast with previous evolutionary models, however, the most parsimonious explanation of these data was that capsule transport genes had been lost in the common ancestor of the meningococcus, gonococcus, and their close relatives, and then reacquired by some meningococci. The most likely donor of the meningococcal transport genes was another Neisseria species.

Molecular characterization of invasive capsule null Neisseria meningitidis in South Africa

Background

The meningococcal capsule is an important virulence determinant. Unencapsulated meningococci lacking capsule biosynthesis genes and containing the capsule null locus (cnl) are predominantly non-pathogenic. Rare cases of invasive meningococcal disease caused by cnl isolates belonging to sequence types (ST) and clonal complexes (cc) ST-845 (cc845), ST-198 (cc198), ST-192 (cc192) and ST-53 (cc53) have been documented. The clinical significance of these isolates however remains unclear. We identified four invasive cnl meningococci through laboratory-based surveillance in South Africa from 2003 through 2013, which we aimed to characterize using whole genome data.

Results

One isolate [NG: P1.7-2,30: F1-2: ST-53 (cc53)] contained cnl allele 12, and caused empyema in an adult male with bronchiectasis from tuberculosis, diabetes mellitus and a smoking history. Three isolates were NG: P1.18-11,42-2: FΔ: ST-192 (cc192) and contained cnl allele 2. One patient was an adolescent male with meningitis. The remaining two isolates were from recurrent disease episodes (8 months apart) in a male child with deficiency of the sixth complement component, and with the exception of two single nucleotide polymorphisms, contained identical core genomes. The ST-53 (cc53) isolate possessed alleles for NHBA peptide 191 and fHbp variant 2; whilst the ST-192 (cc192) isolates contained NHBA peptide 704 and fHbp variant 3. All four isolates lacked nadA. Comparison of the South African genomes to 61 additional cnl genomes on the PubMLST Neisseria database (http://pubmlst.org/neisseria/), determined that most putative virulence genes could be found in both invasive and carriage phenotypes.

Conclusions

Although rare, invasive disease by cnl meningococci may be associated with host immunodeficiency and such patients may benefit from protein-based meningococcal vaccines.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-017-0942-5) contains supplementary material, which is available to authorized users.

Prevalence and detailed mapping of the gonococcal genetic island in Neisseria meningitidis

The 57-kb gonococcal genetic island (GGI) encodes a type IV secretion system (T4SS) that is found in most strains of N. gonorrhoeae. This T4SS functions to secrete single-stranded DNA that is active in natural transformation. The GGI has also been found in some strains of N. meningitidis. We screened 126 isolates of N. meningitidis and found the GGI in 17.5% of strains, with the prevalence varying widely among serogroups. The GGI is found in a significant number of serogroup C, W-135, and X strains but was not found in strains of serogroup A, B, or Y. Through detailed PCR mapping and DNA sequencing, we identified five distinct GGI types in meningococci. DNA sequencing and a genetic assay revealed that the GGI was likely integrated into the meningococcal chromosome by the site-specific recombinase XerCD and that the GGI can be excised and lost from the genome. Functional studies showed that in contrast with the gonococcal T4SS, the meningococcal T4SS does not secrete DNA, nor does it confer Ton-independent intracellular survival. Deletion of T4SS genes did not affect association with or invasion of host cells. These results demonstrate that the GGI is found in a significant proportion of meningococcal strains and that while some strains carry multiple insertions and deletions in the GGI, other strains carry intact T4SS genes and may produce functional secretion systems.

Development of a multiplex PCR assay for detection and genogrouping of Neisseria meningitidis

Neisseria meningitidis is a leading pathogen of epidemic bacterial meningitis and fulminant sepsis worldwide. Twelve different N. meningitidis serogroups have been identified to date based on antigenic differences in the capsular polysaccharide. However, more than 90% of human cases of N. meningitidis meningitis are the result of infection with just five serogroups, A, B, C, W135, and Y. Efficient methods of detection and genogrouping of N. meningitidis isolates are needed, therefore, in order to monitor prevalent serogroups as a means of disease control and prevention. The capsular gene complex regions have been sequenced from only seven out of the 12 serogroups. In this study, the capsular gene complexes of the remaining five serogroups were sequenced and analyzed. Primers were designed that were specific for N. meningitidis species and for the 12 individual serogroups, and a multiplex PCR assay using these specific primers was developed for N. meningitidis detection and genogrouping. The assay was tested using 15 reference strains covering all 12 serogroups, 143 clinical isolates, and 21 strains from closely related species or from species that cause meningitis. The assay could detect N. meningitidis serogroups and was shown to be specific, with a detection sensitivity of 1 ng of genomic DNA (equivalent to ∼4 × 10(5) genomes) or 3 × 10(5) CFU/ml in noncultured mock cerebrospinal fluid (CSF) specimens. This study, therefore, describes for the first time the development of a molecular protocol for the detection of all N. meningitidis serogroups. This multiplex PCR-based assay may have use for the clinical diagnosis and epidemiological surveillance of N. meningitidis.

Comparative overview of the genomic and genetic differences between the pathogenic Neisseria strains and species

The availability of complete genome sequences from multiple pathogenic Neisseria strains and species has enabled a comprehensive survey of the genomic and genetic differences occurring within these species. In this review, we describe the chromosomal rearrangements that have occurred, and the genomic islands and prophages that have been identified in the various genomes. We also describe instances where specific genes are present or absent, other instances where specific genes have been inactivated, and situations where there is variation in the version of a gene that is present. We also provide an overview of mosaic genes present in these genomes, and describe the variation systems that allow the expression of particular genes to be switched ON or OFF. We have also described the presence and location of mobile non-coding elements in the various genomes. Finally, we have reviewed the incidence and properties of various extra-chromosomal elements found within these species. The overall impression is one of genomic variability and instability, resulting in increased functional flexibility within these species.

Many carried meningococci lack the genes required for capsule synthesis and transport

Of 830 Neisseria meningitidis isolates obtained from healthy carriers in Bavaria, Germany, 136 (16.4%) lacked the operons necessary for the synthesis, lipid modification, and transport of capsular polysaccharide. These operons were replaced by a non-coding intergenic region either 113 or 114 bp in length, termed here the capsule null locus (cnl). Comparisons of the nucleotide sequence of this region in the meningococcus and its acapsulate relatives, Neisseria gonorrhoeae and Neisseria lactamica, revealed six distinct sequence variants (cnl-1 to cnl-6), with a total of 10 nucleotide substitutions and three indels. With the exception of one 4 bp insertion, which was unique to a gonococcal isolate, all of the individual sequence changes were present in the N. lactamica isolates examined. The meningococcal isolates with a cnl belonged to one of four otherwise genetically diverse genetic groupings: the ST-53 and ST-1117 complexes (75 isolates); the ST-845 complex (12 isolates); the ST-198 and 1136 complexes (46 isolates), and the ST-44 complex (one isolate). These data demonstrated that a substantial proportion of carried meningococci were incapable of capsule production, that the cnl circulated within Neisseria populations by horizontal genetic exchange, and that the expression of a polysaccharide capsule was not a requirement for person-to-person transmission of certain meningococcal lineages.

Characterization of the CC chemokine receptor 3 on human keratinocytes

CC chemokine receptors are expressed on hematopoietic cells, and these may impart selective homing of monocyte, leukocyte, and lymphocyte subsets to sites of inflammation. CC chemokine receptor 3 is the major receptor on eosinophils and is also expressed on other inflammatory cells suggesting its important role for allergic diseases such as atopic dermatitis and bronchial asthma. Eotaxin, eotaxin-2 and eotaxin-3 have been identified as ligands that only activate CC chemokine receptor 3. CC chemokine receptor 3 is also activated by other promiscuous ligands, however, such as RANTES and monocyte chemotactic protein 4. To date, CC chemokine receptor 3 has not been reported to be expressed on nonhematopoietic cells. In this study, we investigated whether keratinocytes possess autocrine and paracrine mechanisms for CC chemokine secretion and receptor expression as reported for the expression of interleukin 8 and its receptors. Reverse transcriptase polymerase chain reaction analysis demonstrated that CC chemokine receptor 3 mRNA is expressed constitutively in cultured keratinocytes. The signal quantities of the CC chemokine receptor 3 amplicons showed lower intensities for keratinocytes than for eosinophils. In situ hybridization techniques exhibited that basal cell layers of the epidermis were stained homogeneously for CC chemokine receptor 3 mRNA with a decreasing signal to the upper epidermis showing that differentiating and proliferating keratinocytes did express mRNA specific for CC chemokine receptor 3. Immunohistochemical studies confirmed low expression of CC chemokine receptor 3 protein on epidermal keratinocytes compared to the high level observed on infiltrating eosinophils. Furthermore, stimulation of cultured keratinocytes with eotaxin resulted in an increased [3H]thymidine incorporation indicating a role of CC chemokine receptor 3 in epidermal proliferation and differentiation. These data demonstrate that CC chemokine receptor 3 is expressed not only on hematopoietic cells but also on keratinocytes as nonhematopoietic cells with ectodermal origin. Therefore, the identification of CC chemokine receptor 3 on epidermal keratinocytes may indicate a role for CC chemokine receptor 3 and its ligands in skin physiology and pathophysiology.

exl, an exchangeable genetic island in Neisseria meningitidis

The genetic structure and evolution of a novel exchangeable meningococcal genomic island was defined for the important human pathogen Neisseria meningitidis. In 125 meningococcal strains tested, one of three unrelated nucleotide sequences, designated exl (exchangeable locus), was found between a gene required for heme utilization, hemO, and col, encoding a putative Escherichia coli collagenase homologue. The 5' boundary of each exl cassette was the stop codon of hemO, whereas the 3' boundary was delineated by a 33-bp repeat containing neisserial uptake sequences located downstream of col. One of the three alternative exl cassettes contained the meningococcal hemoglobin receptor gene, hmbR (exl3). In other meningococcal strains, hmbR was absent from the genome and was replaced by either a nucleotide sequence containing a novel open reading frame, exl2, or a cassette containing exl3. The proteins encoded by exl2 and exl3 had no significant amino acid homology to HmbR but contained six motifs that are also present in the lipoprotein components of the lactoferrin (LbpB), transferrin (TbpB), and hemoglobin-haptoglobin (HpuA) uptake systems. To determine the evolutionary relationships among meningococci carrying hmbR, exl2, or exl3, isolates representing 92 electrophoretic types were examined. hmbR was found throughout the population structure of N. meningitidis (genetic distance, >0.425), whereas exl2 and exl3 were found in clonal groups at genetic distances of <0.2. The commensal neisserial species were identified as reservoirs for all of the exl cassettes found in meningococci. The structure of these cassettes and their correlation with clonal groups emphasize the extensive gene pool and frequent horizontal DNA transfer events that contribute to the evolution and virulence of N. meningitidis.

The evolution of human pathogens: examples and clinical implications

Recent advances in sequencing of complete bacterial genomes, molecular typing of micro-organisms, and research on microbial pathogenicity factors changed our view on the evolution of human bacterial pathogens. We review current evolutionary concepts on plague and meningococcal disease to illustrate the interplay of molecular phylogeny, epidemiology, and pathogenicity research. Furthermore, examples of the tremendous velocity of bacterial evolution under changing environmental conditions will be discussed.

Microbial relatives of the seed storage proteins of higher plants: conservation of structure and diversification of function during evolution of the cupin superfamily

This review summarizes the recent discovery of the cupin superfamily (from the Latin term "cupa," a small barrel) of functionally diverse proteins that initially were limited to several higher plant proteins such as seed storage proteins, germin (an oxalate oxidase), germin-like proteins, and auxin-binding protein. Knowledge of the three-dimensional structure of two vicilins, seed proteins with a characteristic beta-barrel core, led to the identification of a small number of conserved residues and thence to the discovery of several microbial proteins which share these key amino acids. In particular, there is a highly conserved pattern of two histidine-containing motifs with a varied intermotif spacing. This cupin signature is found as a central component of many microbial proteins including certain types of phosphomannose isomerase, polyketide synthase, epimerase, and dioxygenase. In addition, the signature has been identified within the N-terminal effector domain in a subgroup of bacterial AraC transcription factors. As well as these single-domain cupins, this survey has identified other classes of two-domain bicupins including bacterial gentisate 1, 2-dioxygenases and 1-hydroxy-2-naphthoate dioxygenases, fungal oxalate decarboxylases, and legume sucrose-binding proteins. Cupin evolution is discussed from the perspective of the structure-function relationships, using data from the genomes of several prokaryotes, especially Bacillus subtilis. Many of these functions involve aspects of sugar metabolism and cell wall synthesis and are concerned with responses to abiotic stress such as heat, desiccation, or starvation. Particular emphasis is also given to the oxalate-degrading enzymes from microbes, their biological significance, and their value in a range of medical and other applications.

The opcA and (psi)opcB regions in Neisseria: genes, pseudogenes, deletions, insertion elements and DNA islands

Previous data have indicated that the opc gene encoding an immunogenic invasin is specific to Neisseria meningitidis (Nm) and is lacking in Neisseria gonorrhoeae (Ng). The data presented here show that Nm and Ng both contain two paralogous opc-like genes, opcA, corresponding to the former opc gene, and (psi)opcB, a pseudogene. The predicted OpcA and OpcB proteins possess transmembrane regions with conserved non-polar faces but differ extensively in four of the five surface-exposed loops. Gonococcal OpcA was expressed weakly under in vitro conditions, and it is unknown whether these bacteria can express this protein at high levels. Analysis of the sequences flanking opcA and (psi)opcB revealed a framework of conserved housekeeping genes interspersed with DNA islands. These regions also contained several pseudogenes, deletions and IS elements, attesting to considerable genome plasticity. Both opcA and (psi)opcB are located on DNA islands that have probably been imported from unrelated bacteria. A third island encodes the dcmD/dcrD R/M genes in Ng versus a small open reading frame in most strains of Nm. Rare strains of Nm were identified in which the R/M island has been imported. DNA islands in Nm and Ng seem to have been acquired by recombination via conserved flanking housekeeping genes rather than by insertion of mobile genetic elements.

Genetic basis for biosynthesis, structure, and function of meningococcal lipooligosaccharide (endotoxin)

The exclusive human pathogen Neisseria meningitidis expresses lipooligosaccharide (LOS), an endotoxin that is structurally distinct from the lipopolysaccharides (LPS) of enteric Gram-negative bacilli. Differences that appear to be biologically important occur in the composition and attachment of acyl chains to lipid A, phosphorylation patterns of lipid A, and the incorporation and phosphorylation of sugar residues in the LOS inner core. Further, unlike most enteric LPS, only two to five sugar residues are attached to the meningococcal LOS inner core, and there are no multiple repeating units of O-antigens. In contrast to Escherichia coli, where the LPS biosynthesis genes are organized as large operons, the meningococcal LOS biosynthesis genes are organized into small operons or are located individually in the chromosome. Some of these genetic loci in meningococci and gonococci display polymorphisms caused by localized chromosomal rearrangements. One mechanism of antigenic variation of meningococci LOS is the regulation of glycosyltransferase activity by slipped strand mispairing of homopolymeric tracts within the 5' end of the genes encoding these enzymes, resulting in the addition of different sugar residues to the LOS molecule. Meningococcal LOS is a critical virulence factor in N. meningitidis infections and is involved in many aspects of pathogenesis, including the colonization of the human nasopharynx, survival after bloodstream invasion, and the inflammation associated with the morbidity and mortality of meningococcemia and meningitis. Meningococcal LOS, which is a component of serogroup B meningococcal vaccines currently in clinical trials, has been proposed as a candidate for a new generation of meningococcal vaccines. The rapidly expanding knowledge of the genetic basis for biosynthesis, structure, and regulation of meningococcal LOS provides insights into unique endotoxin structures and the precise role of LOS in the pathogenesis of meningococcal disease.

Cutting Edge: Detection of MCP-4 in Dermal Fibroblasts and Its Activation of the Respiratory Burst in Human Eosinophils

CC-chemokines are an important family of proinflammatory mediators that promote the recruitment and activation of human eosinophils in chronic inflammatory diseases. Recently, a novel human CC-chemokine, monocyte chemotactic protein 4 (MCP-4), has been reported that shows amino acid sequence similarities with eotaxin and RANTES, induces chemotaxis of eosinophils, and signals through specific chemokine receptors. In this study, we investigated the effect of MCP-4 on different eosinophil effector functions leading to the activation of the respiratory burst. In human eosinophils, MCP-4 dose dependently induced the production of reactive oxygen species and actin polymerization as a related event. Pretreatment of eosinophils with different enzyme inhibitors interacting with the signal transduction cascade revealed that Gi protein, protein kinase C, tyrosine kinase, and phosphatidylinositol-3-kinase are involved in the signaling following stimulation with MCP-4. In addition, cytokine-stimulated human dermal fibroblasts expressed high levels of MCP-4 mRNA, suggesting that fibroblasts are a physiologic source of MCP-4. Therefore, this study demonstrates that there is an important role of MCP-4 in the activation of eosinophils and that the interaction between dermal fibroblasts and human eosinophils may play an important role within the cytokine network.

The Neisseria gonorrhoeae S.NgoVIII restriction/modification system: a type IIs system homologous to the Haemophilus parahaemolyticus HphI restriction/modification system

Strains of Neisseria gonorrhoeae possess numerous restriction-modification (R-M) systems. One of these systems, which has been found in all strains tested, encodes the S. NgoVIII specificity (5'TCACC 3') R-M system. We cloned two adjacent methyltransferase genes (dcmH and damH), each encoding proteins whose actions protect DNA from digestion by R.HphI or R.Ngo BI (5'TCACC 3'). The damH gene product is a N 6-methyladenine methyltransferase that recognizes this sequence. We constructed a plasmid containing multiple copies of the S.NgoVIII sequence, grew it in the presence of damH and used the HPLC to demonstrate the presence of N 6-methyladenine in the DNA. A second plasmid, containing overlapping damH and Escherichia coli dam recognition sequences in combination with various restriction digests, was used to identify which adenine in the recognition sequence was modified by damH. The predicted dcmH gene product is homologous to 5-methylcytosine methyltransferases. The products of both the dcmH and damH genes, as well as an open reading frame downstream of the damH gene are highly similar to the Haemophilus parahaemolyticus hphIMC , hphIMA and hphIR gene products, encoding the Hph I Type IIs R-M system. The S.NgoVIII R-M genes are flanked by a 97 bp direct repeat that may be involved in the mobility of this R-M system.

A new gene locus of Bordetella pertussis defines a novel family of prokaryotic transcriptional accessory proteins

Recently, a novel type of regulatory mutation causing differential effects on the expression of virulence genes due to a slight overexpression of the RNA polymerase alpha subunit (RpoA) was found in Bordetella pertussis (N. H. Carbonetti, T. M. Fuchs, A. A. Patamawenu, T. J. Irish, H. Deppisch, and R. Gross, J. Bacteriol. 176:7267-7273, 1994). To gather information on the molecular events behind this phenomenon, we isolated suppressor mutants of the RpoA-overexpressing strains after random mutagenesis. Genetic characterization of these suppressor strains revealed the existence of at least three distinct groups of dominant alleles. Mutations occurred either in the rpoA locus itself, in the bvg locus, or in unknown gene loci. One mutant of the latter group was further characterized. By the introduction of a cosmid library containing genomic B. pertussis DNA into this suppressor strain, we isolated a cosmid which suppressed the phenotype of the suppressor strain, thus restoring the negative effect on transcription of the ptx and cya toxin genes. Mutagenesis of the cosmid with Tn5 led to the identification of the gene locus responsible for this phenomenon. Its DNA sequence revealed the presence of an open reading frame (ORF) consisting of 2,373 bp coding for a hypothetical 86-kDa protein with extensive sequence similarities to ORFs with not yet identified functions of Escherichia coli, Haemophilus influenzae, and Neisseria meningitidis. The new gene, termed tex, for toxin expression, seems to be an essential factor for B. pertussis, as it cannot be deleted from the bacterial chromosome. All members of this new protein family show significant sequence similarities with the mannitol repressor protein MtlR and with the presumptive RNA-binding domains of the Pnp and ribosomal S1 proteins of E. coli in their N- and C-terminal parts, respectively. These sequence similarities and the fact that the tex gene was isolated by virtue of its effects on gene expression in B. pertussis indicate that the members of this new protein family may play an important role in the transcription machinery of prokaryotic organisms.